Optimal Thermolysis Conditions for Soil Carbon Storage on Plant Residue Burning: Modeling the Trade-Off between Thermal Decomposition and Subsequent Biodegradation

Abstract

Field burning of plant biomass is a widespread practice that provides charred materials to soils. Its impact on soil C sequestration remains unclear due to the heterogeneity of burning products and difficulty in monitoring the material's biodegradation in fields. Basic information is needed on the relationship between burning conditions and the resulting quantity/quality of residue-derived C altered by thermal decomposition and biodegradation. In this study, we thermolyzed residues (rice straw and husk) at different temperatures (200-600°C) under two oxygen availability conditions and measured thermal mass loss, C compositional change by solid-state C NMR spectroscopy, and biodegradability of the thermally altered residues by laboratory aerobic incubation. A trade-off existed between thermal and microbial decomposition: when burned at higher temperatures, residues experience a greater mass loss but become more recalcitrant via carbonization. When an empirical model accounting for the observed trade-off was projected over 10 to 10 yr, we identified the threshold temperature range (330-400°C) above and below which remaining residue C is strongly reduced. This temperature range corresponded to the major loss of O-alkyl C and increase in aromatic C. The O/C molar ratios of the resultant residues decreased to 0.2 to 0.4, comparable to those of chars in fire-prone field soils reported previously. Although the negative impacts of biomass burning need to be accounted for, the observed relationship may help to assess the long-term fate of burning-derived C and to enhance soil C sequestration.

Distinctive Roles of Two Aggregate Binding Agents in Allophanic Andisols: Young Carbon and Poorly-Crystalline Metal Phases with Old Carbon

“…Among the low-density fractions (F1-F2), ∆ 14 C was negatively correlated with the aromaticity index based on solid-state 13 C NMR spectroscopy (ratio of aromatic-C to O-alkyl-C, r 2 = 0.79, p < 0.001, using data from [53]) as well as with C:N ratio (Figure 2b). Burning and charring of plant residues increase their aromaticity, and remaining materials have higher stability against microbial degradation [62][63][64]. Thus, these negative correlations in F1-F2 suggest the presence of old pyrogenic, thus recalcitrant C. This interpretation is further supported by the high abundance of shiny dark-colored fragments in mixture with decaying plant litter based on light microscopic observation in F2 of Till-1 soil [42].…”

Impacts of soil incorporation of pre-incubated silica-rich rice residue on soil biogeochemistry and greenhouse gas fluxes under flooding and drying

“…for husk and ~0.6% for straw (Kajiura et al, 2015). Ashed husk residues were obtained from a mill in Battambang, Cambodia where fresh husk is used as a fuel source and incompletely combusted at ~450° C, as is done in some rice-growing countries (Haefele et al, 2009;Savant et al, 1997b).…”

Effects of bamboo biochar application on global warming in paddy fields in Ehime prefecture, Southern Japan

“…produced under the higher temperature and low-oxygen concentration shows higher tolerance for decomposition (Kajiura et al 2015), CO 2 and CH 4 emission induced by biochar might be mitigated using decomposition-resistant biochar. Generally, biochar has porous micro-space (Nguyen et al 2004;Yu et al 2006) and biochar application can improve soil water holding properties (Rondon et al 2006).…”

“…Because applied biochar in this study was produced at relatively high temperature, it was assumed that the biochar contained little decomposable C. Kajiura et al (2015) simulated that biochar made by rice straw and husk under high temperature (> 500°C) was hardly decomposed for 1000 years. Our study, however, indicated that biochar produced under high temperatures potentially contains decomposable C in field conditions, though the material of the biochar in their study was different than in Kajiura et al (2015). Moreover, the higher decomposition rate of biochar C in this study might also result in the acceleration of the microbial activity by biochar application.…”

“…Biochar application to soil is a carbon (C) recovery and storage technique for sequestrating atmospheric CO 2 and is expected to decrease atmospheric CO 2 concentrations (Uchimiya and Hiradate 2013). Biochar produced under higher temperatures and lower oxygen concentrations shows higher tolerance for decomposition in soil (Kajiura et al 2015). It has been shown that biochar application to fields improves soil conditions for CH 4 oxidizers (van Zwieten et al 2009), while the impact of biochar application on GHG from soil depends on the type of the materials, and pyrolysis conditions.…”